Ecuador is prepared to set up an operating theatre in its London embassy if Julian Assange needs urgent medical attention and the UK is not prepared to guarantee his safe passage to a hospital and back, according to the Ecuadorean foreign minister.

As the WikiLeaks founder spent his 100th day in the Ecuadorean embassy, where he has sought refuge from extradition to Sweden to face allegations of sexual crimes, the country's foreign minister met his British counterpart, William Hague, to ask about contingency plans should Assange fall ill.

Hague told Ricardo Patino that he would consult officials and lawyers and respond within a few days, but a British official commented: "Maybe the Ecuadoreans should have thought of that before they granted him asylum." The official added that British police were under obligation to arrest Assange as soon as he stepped out of the embassy.

"One thing we have proposed is to have an ambulance parked outside," Patino told the Guardian in an interview in New York. "What we have said, if such a case should happen, we should be ready to install an operating theatre inside the premises, unless Mr Hague responds, as he promised in the next few days, that he [Assange] would be able to go to a hospital."

The Ecuadorean foreign minister said that the Australian government had offered to help organise Assange's healthcare during an indefinite stay in an embassy apartment, given the diplomatic impasse over his fate. Ecuador offered him asylum last month, saying he faced political persecution in the US, but the UK insists it has a legal duty to arrest him and extradite him to Sweden to face questioning. Australian officials have not confirmed Patino's claim that Canberra had offered medical help.

When Assange addressed diplomats at the UN general assembly this week, via a satellite link from the London embassy, he appeared pale, with dark rings under his eyes. His voice was hoarse and his sniffed frequently.

Patino said he was not aware of any immediate health concerns for Assange but added: "We know that anyone who lives in these conditions of confinement may easily suffer from health issues, not only physical but also psychological. Imagine you have to stay in a room for three months. Imagine if you are going to be five years in this confinement."

In November 2010, a Swedish court ordered Assange be detained for questioning after allegations by two women that what had started as consensual sex had turned non-consensual.

This week, Amnesty International called on Sweden to provide a guarantee that if Assange travelled there to answer questions over the sex-crime allegations, he would not be sent on to the US for charges connected to WikiLeaks' publication of thousands of US diplomatic and military cables.

A spokeswoman for the Swedish foreign ministry said the country's legislation did not allow any judicial decision like extradition to be predetermined. The UK, which would also have to permit an extradition to the US, has given the same response but Hague stressed to Patino at their New York meeting that the European Convention on Human Rights sets strict limits on such extraditions, forbidding them, for example, if the charges in question carry the death penalty.

"The foreign secretary described the extensive human-rights safeguards in UK extradition law. He requested the government of Ecuador to study these provisions closely in considering the way ahead," a foreign office spokesman said.

Officials said that the treatment of the alleged source of the WikiLeaks US cables, Bradley Manning – an American soldier whose lawyers say was subject to brutal and humiliating treatment and who has so far spent more than two years in jail without trial – would be taken into account if and when any future extradition decision was made.

However, Patino said that it was too late for such assurances, since Ecuador's decision to offer asylum was irrevocable.

"When we hadn't yet granted asylum, we could talk about guarantees," the foreign minister said. "Now that we have granted asylum we are under the obligation not to surrender Mr Assange."